1. Field of the Invention
This invention relates to a system for controlling a number of bits required to represent coded output data.
2. Description of the Prior Art
A highly efficient encoding system for compressing the number of bits representing particular data is used in various apparatuses such as a communication apparatus, a recording and reproducing apparatus, and a display apparatus. Some of such encoding systems output variable-length codes. Generally, it is desirable that the codes are outputted from an encoding system at essentially a constant rate.
It is known to control the number of bits of coded data output data from such an encoding system. There are two data amount control systems. In the first data amount control system, the amount of coded output data is held approximately constant by use of entropy encoding and feedback control. In the second data amount control system, the amount of coded output data is held essentially constant by use of adaptive control of a quantization bit number and feedforward control. The second data amount control system is disclosed in Japanese published unexamined patent application No. 63-151269.
The first data amount control system can hold the average of the amount of coded output data essentially constant for a long time but can not surely hold the amount of coded output data equal to or within a prescribed amount for each of short unit periods.
In the second data amount control system, since the data amount per signal block is required to be fixed with respect to a quantizing step size, entropy encoding can not be used so that the efficiency of encoding tends to be inadequate.